Photoflash lamp



Nov. 27, 1956 E. G. F. ARNOTT ETAL 2,771,765

PHOTOFLASH LAMP Filed Sept. 1, 1954 IN VEN TORJ mas 0 7 ram 50M.

Unite PHGTOFLASH LAMP Application September 1, 1954, Serial No. 453,640

5 Claims. (Cl. 67-31) This invention relates to the manufacture of SMtype photoflash lamps and, more particularly, to an improved andsimplified igniter construction.

The present method of igniting the primer in Speed Midget or so-calledSM photofiash lamps, which are lamps having a paste primer with no othercombustible material, such as metal foil, and for which the presentinvention is particularly applicable, consists of passing a currentthrough a fine tungsten filament which is thus heated to incandescence.The filament is mounted on 'two heavier lead wires which are coated witha primer material at the junction of the filament and lead wires. Theheat from the incandescent filament causes a highly exothermic chemicalreaction from which the high intensity flash is derived. The maindifliculties encountered in manufacture and operation are:

(a) Mounting the fine tungsten filament is a painstaking operation.

(/1) The filament will not be heated at a sufficiently rapid rate if thefiashgun batteries are low.

Base contact in the flashgun must be good. Socket contacts must makefirm contact with the corresponding socket lead.

It is the general object of this invention to avoid and overcome theforegoing and other difficulties of and objections to prior artpractices by providing a very positive SM lamp ignition system whereinthe filament is eliminated.

It is another object to simplify the method of manufacturing SMphotoflash lamps so that the bulbs thereof may be exhausted and gasfilled, simultaneously with the connection of plastic bases thereto.

It is a further object to provide an SM lamp primer arrangement which isadapted to be ignited by a high voltage spark discharge.

The aforesaid objects of the invention, and other objeots which willbecome apparent as the description proceeds, are achieved by providingan SM photoflash lamp having a plastic base connected to a bulb andprovided with leads, at least one of which is insulated, and the innerends of which are bridged by a primer. Also provided is a method formanufacturing such a lamp.

For a better understanding of the invention, reference should be had tothe accompanying drawing wherein:

Fig. l is an elevational view of a lamp embodying our invention, acircuit for igniting such a lamp being indicated diagrammatically;

Fig. 2 is a fragmentary axial sectional view of the lamp of Fig. 1, to alarger scale.

Fig. 3 is an expanded, fragmentary, sectional view of the primer-leadportion of the lamp shown in Fig. 2.

Fig. 4 is an elevational view of a modified form of mount for a lampsuch as shown in Fig. 1;

Fig. 5 is an elevational view of another modification of a mount for alamp as shown in Fig. 1.

With specific reference to the form of the invention illustrated in thedrawing, in first considering Figs. 1, 2

States Patent and 3, there is shown a photoflash lamp 21 comprising anenvelope or bulb 22 of radiation-transparent material such as glass. Theedge of the neck 23 of said bulb 22 is embedded in a plastic blockforming a base 24. A pair of leads 25 and 26, are employed, the latterextending through the base 24 to provide a center contact 20. The formeris shown bare, and extends from a side of the base, where it forms alateral prong 27. The prong 27 may unite with a side plate, such asillustrated in Fig. 15 of copending Rively application Ser. No. 358,-415, filed May 29, 1953, and owned by the assignee of the presentapplication, and designated by the character 75, 'or with a band, suchas that designated by the reference character of Fig. 17 of thecopending Rively application.

The portion of the lead 26 interior of the bulb 22 and which extendsabove the plastic of the base 24, is coated with porous insulatingmaterial 35 of any desired character, such as the oxide of the metalitself. The lead 25 may be similarly insulated, if desired, but this isnot essential. This insulating material is desirably provided by formingthe lead 26 of aluminum, or with 'an aluminum surface, which is oxidizedto form an adherent coating of porous aluminum oxide. Other possiblebase metals are nickel, tantalum and other suitable metals, the oxide ofwhich is insulating. Alternatively, a dielectric other than an oxide ofthe base metal may be coated onto the high voltage lead, providing ofcourse that such a dielectric has a relatively low breakdown strength tofacilitate the setting up of the spark discharge. For example, graphitemay be embedded in polystyrene or methyl methacrylate and coated ontoone or both of the leads.

Connecting the inner ends of the lead 25 and 26, which are desirablybent to point toward one another, is disposed a mass of primer material28, which may be conventional such as a paste formed of zirconiumpowder, or other suitable metal, and an oxidizing agent, therebycompleting the mount 30. The bulb 22, the neck of which is cemented tothe base by the plastic material of the base 24, also encloses anatmosphere of oxygen or other combustion-supporting gas such as asuitable oxide of nitrogen, for example.

The invention may be described, using aluminum as an example, but othersuitable metals can be treated in a similar manner. The oxide-coatedlead or leads is (or are) prepared by an anodizing process in which alength of aluminum wire is made the anode and an inert electrode is madethe cathode. The electrolyte is about 0.1 molar sulfuric acid. A currentof 2-3 amps. at 30 volts is passed for about 15 secs. at which time thewire is withdrawn, washed with hot water, and then air dried. Thiscoated wire is then mounted along with a length of uncoated aluminumwire. Primer is applied so that the dried bead bridges the gap and makescontact with both leads. The assembly is then mounted in a lamp. Inoperation the oxide-coated lead may be connected to the high voltagesource and the other lead to ground. The anodizing process, asdescribed, will produce an aluminum oxide coating of about 1 milthickness, which is the preferred thickness for such a coating, althoughthe oxidedielectric coating may vary between about 0.5 mil and 5 milsthickness. Below 0.5 mil thickness the coating tends to becomediscontinuous so that the coated primer may contact the aluminum basemetal of the lead. Above- 5 mils thickness the aluminum oxide tends tochip off thus creating low resistance paths and eliminating the sparkdischarge.

As a specific embodiment, the leads 25 and 26 may project /2 above thebase 24 into the bulb and these leads are preferably separated by /2",except at their inwardly projecting extremes, to insure against a sparkPatented Nov. 27, 1956 dischargebetween theleads at. any point otherthan at their inner ends. The lead inner ends may have a gaptherebetween of A", for example. This dimension is not critical-providedsomegap is maintained, -and this dimension is more governed .by propersuspension of the primer bead 28. '50 mg. of primermaterial may besuspended between the inwardly extending portions of; the leads and thisprimer material may consist of a mixture of zirconium powder andpotassium perchlorate-inthe proportion of 75-25. The envelope mayenclose an oxygen atmospher at a pressure of 600 mm. Other suitablematerials may be used as a primer such as powdered magnesiumandanoxidizer, for example.

The wiringndiagramofFig. 1 indicates how the. lamp there illustrated maybe fired. in this diagram, the reference. 31 represents; arsource ofpower, which may be a 22 /2 volt hearing-aid dry cell battery. Connectedto the battery is a resistor 32, of preferably about 10,000 ohms, and acondenser 33,- of preferably. about 50 microfarads capacity,saidcondenser being across the battery terminals with the. resistor inseries.

The condenser terminals are, in turn, connected through a switch 34 tothe primarywinding'36 of'a step-up transformer 37. The secondary winding38 of said transformer has one terminal connected toa terminal of theprimary winding 36, and the otherterminal connected to. the insulatedlead 26 at the router contact portion thereof at the center of thebase-24 of the lamp 21. The prong 27 may be grounded, asindicated at 39,if desired. With this arrangement, the condenser is slowly chargedthrough the resistor 32 and is in condition for delivering a desiredsurge of electrical energy to the primary winding 36 of the transformerupon closing the switch 34.

The ratio between the turns of vthe primary and secondary windings isdesirablysuch that a potential of at least 10,000 volts and preferably20,000 volts is delivered to the base 24 on closing the switch 34, tothereby produce a spark discharge between the inner end of the lead 26and the primer material 28, across the gap consisting of the porousdielectric material 35, thereby igniting the primer.

Although wehave diagrammatically disclosed means for igniting a lampembodying this invention, yet practical embodiments of such means are.illustrated in Figs..5 and 6 of the copending application of Rively,previously referred to.

The mount 30 shown in Fig. 3 is like the mount 30 of Figs. 1 and 2,except that both of the leads 25 and 26 extend from the base 24 towardone another, to their inner ends which are bridged by a mass of primer28 Also, both are shown coated with porous insulating material 35although only one lead need be so coated. Such a mount may be assembledwith a bulb to make a photofiash lamp like the mount 30 of Figs. 1, 2and 3,

The mount 30* shown in Fig. 4 is like the mount 30 of Figs. 1, 2 and 3,except that both of the leads 25 and 26 arecoated with a porousinsulating material 35 only at their inwardly projecting extremitieswhere the mass of primer 28 is supported. Such a mount when incorporatedinto a lamp, as shown in Fig. 1, will function exactly the same sinceonly that portion of the leads about which the primer is tobe coatedneed be provided with an insulating or dielectric coating. Also theleads 25 and 26 traverse the base in a substantially parallel fashion,terminating in the bottom of the base in two contact electrodes 40 and.1, across which the igniting potential is applied. It should be notedthat for manufacturing convenience the entire portion of at least onelead which projects into the bulb may be provided with adielectriccoating. This eliminates the need for accurate positioning ofthe lead when applying the dielectric coating thereto.

Normally where: dielectricsare employed their purpose is. to insure.against a. breakdown and to insure that a spark discharge is not set up.In the instant application,

however, the dielectric is so applied as to insure that a sparkdischarge will be set up and that the dielectric will break down.Aluminum oxide is particularly adapted as a dielectric in the instantapplication, for microscopic examination of a 1 mil coating of aluminumoxide reveals that there exists a plurality of crevices or rifts in thealuminum oxide which crevices parallel the length dimension of the wireelectrode. These crevices are of no more than 1 micron in width andoccur on an average of about one every 50 mircons when the dielectriccoating is prepared in the previously described manner. When the primermaterial is coated onto the anodized aluminum lead the surface tensionof the primer is suflicient that these crevices or rifts in the aluminumoxide coating will not be filled, but will-be bridged by the primer.Thus, there exists through the aluminum oxide coating a series of airgaps which are particularly adapted to facilitate the setting up of aspark discharge through the dielectric.

In the operation of the lamps of this invention one of the leads onfiring is at a very high potential and the other lead is at groundpotential. If the dielectric coating is applied either to both leads orto the high potential lead, the primer head will in efiect be at groundpotential since-the primer is a relatively good conductor. Thedielectric coating will break down under the applied voltage and a sparkdischarge will be formed. The primer bead is suspended between twoleads, as hereinbefore explained, and when drying the weight of the beadapparently causes stress pores, fissures or rifts to occur inthe primerbead, whichpores extend through the bead front one lead to the other bymeans of devious stress paths. These pores constitute paths throughwhich oxygen may be supplied to the vicinity of spark discharge, whichis set up at the dielectric-primer interface, to initiate firing of theprimer.

The breakdown voltage for the dielectric coating should not exceed about1000 volts where the applied potential is- 10,000 to 20,000 volts iffiring of the lamp is to be reproducible. Itshould be understood thatunder ideal conditions the breakdown strength for the dielectric mightbeashigh as .of the voltage which is availableto create the spark, butunder such conditions a reproducible spark. cannot be obtained. 'Theminimum breakdown strength for the dielectric should be not less thanthe dielectric strength of the air and the minimum breakdown strengthfor the dielectric as used in this application should be at least volts.It should be understood that these dielectric breakdown strengthlimitations are only given for a practical working embodiment and can beexceeded in either extreme under ideal conditions, which are not readilyreproducible on a production basis.

A lamp such as illustrated in Fig. 1 is desirably manu factured usingapparatus such as illustrated in. Figs. '13 and l4 of said Rivelyapplication. The plastic material desirably employed. to make the base24 may be that designated by the trademark Vinnapas. This is so-calledsealing" plastic manufactured by Dr. Alexander Wacker, Gesellschaft furElectrochemisch Industrie, G. m. b. H., 22 Prinzregentenstrasse, Munich,Germany. This is 45% polyvinyl acetate, 25% powdered talc and 30%microcrystalline wax. However, other solid plastic materials which havemelting points lower than that of the bulb 22 to which connected, andlow enough to permit softening prior to ignition of the primer 28, maybe employed, as by melting and casting to shape.

The apparatus of Fig. 12 of the -Rively application referred to mayserve for applying primer to the leads 25 and 26, although it will beunderstood that such primer may be applied in any desired manner as iswell understood by-those skilled in the art.

After application of the pasteprimer28 to the leads 25 and 26 over thedielectric coating 35 on thelatter, the primer is allowed to dry andthe'mount so constructed isthenrevcrsed :in position. The base 24 maybe.insorted in a cup. such as designated 59 mounted on'th'e upper end of areciprocable rod 61 and carrying a light spring 62 in its interior, asillustrated in the copending Rively application, hereinbefore referredto. The spring 62 resiliently urges a disk into engagement with thebottom of a supported base 24. The cup is disposed in an exhausting andgas-filled chamber 63, which for the purpose is connected to an exhaustand gas-filling system, as by means of a pipe 64. Leakage between therod 61 and the lower wall of the chamber is prevented by means of asealing bellows arrangement 65, desirably the so-called sylphon type.

In the chamber 63, as illustrated in said copending Rively application,is mounted a coil of oxygen-resisting Nichrome or other heating wire 66,surrounding the cup 59. Leads 67 and 68 connect the wire 66 to a sourceof power by energizing the same to soften quickly the plastic base 24,without igniting the primer 28, while said base is supported resilientlyin the cup 59. The chamber 63 opens upwardly and is closed partially bya rubber or other resilient cover 69, apertured as indicated at 71 toreceive the neck 23 of the bulb 22, while nesting with the main orbulbular portion thereof to provide an air-tight engagement.

The manner of operating the apparatus of said copending application foruniting a base to a bulb after exhausting and gas-filling is as follows:A mount comprising a plastic base 24 and leads 25 and 26, at least oneof which is oxidized or otherwise insulated, carrying a mass of primermaterial 28, is placed with the base resting on the spring 62 anddisposed in the cup 59. A bulb 22 is then placed over the primer 28 toclose the aperture 71. The air in the chamber 63 and connected bulb 22is then exhausted, while the coil 66 is energized to soften the plasticbase 24.

After exhausting to the desired extent, oxygen or othercombustion-supporting gas is introduced into the chamber 63 from whenceit passes to the bulb 22. The bulb during the operation is held in placeby a suitable chuck 72. When filling gas at the desired pressure hasbeen introduced and the plastic base 24 sufiiciently softened, the rod61 is raised to push the base 24 into sealing engagement with the lowerend of the neck of the bulb. The apparatus and formed lamp are thenallowed to cool and the lamp removed and replaced by parts of otherlamps for a repetition for the operation.

It will be recognized that the objects of the invention have beenachieved by providing a very positive SM type photoflash lamp whereinthe filament is eliminated and in which the primer is ignited by a highvoltage spark. Also provided is a method for making such lamps.

While in accordance with the Patent Statues, one best known embodimentof the invention has been illustrated and described in detail, it is tobe understood that the invention is not limited thereto or thereby.

We claim:

1. A photoflash lamp comprising a radiation-transmitting bulb with aneck, a block of plastic forming a base in which the edge of said neckis embedded, a pair of spaced metallic leads traversing said base andprojecting inwardly within said bulb, a dielectric coating on at leastone of the inwardly projecting extremities of said leads, a paste primersupported by and between said lead inwardly projecting extremities andin contact therewith, said dielectric coating insulating the metallicportions of the said dielectric coated lead portions from said pasteprimer, and a combustion supporting atmosphere contained within saidbulb.

2. A photoflash lamp comprising a radiation-transmitting bulb with aneck, a block of plastic forming a base in which the edge of said neckis embedded, a pair of spaced metallic leads traversing said base andprojecting inwardly within said bulb, a dielectric coating on theinwardly projecting extremity of one of said leads, a paste primersupported by and between said lead inwardly projecting extremities andin contact therewith, said dielectric coating insulating the metallicportion of said dielectric coated inwardly projecting lead extremityfrom said paste primer, and a combustion supporting atmosphere containedwithin said bulb.

3. A photoflash lamp comprising a radiation-transmitting bulb with aneck, a block of plastic forming a base in which the edge of said neckis embedded, a pair of spaced metallic leads traversing said base andprojecting inwardly within said bulb, a porous dielectric coating on theinwardly projecting extremity of one of said leads, a porous pasteprimer bridging said lead inwardly projecting extremities, saiddielectric coating insulating the metallic portion of said dielectriccoated inwardly projecting lead extremity from said paste primer, and acombustion supporting atmosphere contained within said bulb.

4. A photoflash lamp comprising a radiation-transmitting bulb with aneck, a block of plastic forming a base in which the edge of said neckis embedded, a pair of spaced metallic leads traversing said base andprojecting inwardly within said bulb, dielectric coatings on theinwardly projecting extremities of said leads, a paste primer supportedby and between said lead inwardly projecting extremities and in contacttherewith, said dielectric coatings insulating the metallic portion ofsaid dielectric coated inwardly projecting lead extremities from saidpaste primer, and a combustion supporting atmosphere contained withinsaid bulb.

5. A photoflash lamp comprising a radiation-transmitting bulb with aneck, a block of plastic forming a base in which the edge of said neckis embedded, a pair of spaced aluminum leads traversing said base andprojecting inwardly within said bulb, a dielectric coating of aluminumoxide on the inwardly projecting extremity of one of said leads, aporous paste primer supported by and between said lead inwardlyprojecting extremities and in contact therewith, said dielectric coatinginsulating the metallic portion of said dielectric coated inwardlyprojecting lead extremity from said paste primer, and a combustionsupporting atmosphere contained within said bulb.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PHOTOFLASH LAMP COMPRISING A RADIATION-TRANSMITTING BULB WITH ANECK, A BLOCK OF PLASTIC FORMING A BASE IN WHICH THE EDGE OF SAID NECKIS EMBEDDED, A PAIR OF SPACED METALLIC LEADS TRAVERSING SAID BASE ANDPROJECTING INWARDLY WITHIN SAID BULB, A DIELECTRIC COATING ON AT LEASTONE OF THE INWARDLY PROJECTING EXTREMITIES OF SAID LEADS, A PASTE PRIMERSUPPORTED BY AND BETWEEN SAID LEAD INWARDLY PROJECTING EXTREMITIES ANDIN CONTACT THEREWITH,